Remote Network penetration via NetBios hack/hacking

These are basic techniques but very useful when penetration testing any Windows based network, the techniques were discovered on WinNT but are still very valid on Windows2000 and in some cases Windows2003 due to backwards compatibility.

When targetting a given network, the first thing an intruder would do, would be to portscan the remote machine or network.A lot of information can be gathered by a simple port scan but what the intruder is looking for is an open port 139 – the Default NetBios port.It’s surprising how methodical an attack can become based on the open ports of a target machine.You should understand that it is the norm for an NT machine to display different open ports than a Unix machine.Recently, several tools have been released to fingerprint a machine remotely, but this functionality has not been made available for NT.

Information gathering with NetBIOS can be a fairly easy thing to accomplish, albeit a bit time consuming.

NetBIOS is generally considered a bulky protocol with high overhead and tends to be slow, which is where the consumption of time comes in.

If the portscan reports that port 139 is open on the target machine, a natural process follows. The first step is to issue an NBTSTAT command.

The NBTSTAT command can be used to query network machines concerning NetBIOS information.

It can also be useful for purging the NetBIOS cache and preloading the LMHOSTS file.

This one command can be extremely useful when performing security audits.

Interpretation the information can reveal more than one might think.

Usage: nbtstat [-a RemoteName] [-A IP_address] [-c] [-n] [-R] [-r] [-S] [-s] [interval]











–a    Lists the remote computer‘s name table given its host name.

-A    Lists the remote computer’s name table givenits IP address.

–c    Lists the remote name cache including the IPaddresses.

–n    Lists local NetBIOS names.

–r    Lists names resolved by broadcast and viaWINS.

–R    Purges and reloads the remote cache nametable.

–S    Lists sessions table with the destination IPaddresses.

–s    Lists sessions table conversions.

The column headings generated by NBTSTAT have the following meaning


Number of bytes received.


Number of bytes sent.


Whether the connection is from the computer(outbound)

or from another system to the local computer(inbound).


The remaining time that a name table cacheentry will “live”

before your computer purges it.

Local Name

The local NetBIOS name given to theconnection.

Remote Host

The name or IP address of the remote host.


A name can have one of two types: unique orgroup.

The last byte of the 16 character NetBIOS nameoften

means something because the same name canbe present

multiple times on the same computer. Thisshows the last

byte of the name converted into hex.


Your NetBIOS connections will be shown in oneof the

following “states”:

<strong>State                   Meaning</strong>

Accepting         An incoming connection is inprocess.

Associated        The endpoint for a connection hasbeen created

and your computer has associated itwith an IP


Connected         This is a good state! It meansyou‘re connected

to the remote resource.

Connecting        Your session is trying to resolvethe name–to–IP

address mapping of the destinationresource.


Your computer requested a disconnect, and it is

waiting for the remote computer to do so.

Disconnecting     Your connection is ending.

Idle              The remote computer has been openedin the current

session, but is currently not acceptingconnections.

Inbound           An inbound session is trying toconnect.

Listening         The remote computer is available.

Outbound         Your session is creating the TCPconnection.

Reconnecting      If your connection failed on thefirst attempt,

it will display this state as it tries toreconnect.

Here is a sample NBTSTAT response of my NT Box:

C:\>nbtstat –A

NetBIOS Remote Machine Name Table

Name               Type         Status


MR_B10NDE      <00>  UNIQUE      Registered

WINSEKURE LABS <00>  GROUP       Registered

MR_B10NDE      <03>  UNIQUE      Registered

MR_B10NDE      <20>  UNIQUE      Registered

WINSEKURE LABS <1E>  GROUP       Registered

MAC Address = 44–45–53–54–00–00

Using the table below, what can you learn about the machine?

Name Number Type Usage


<computername> 00 U Workstation Service

<computername> 01 U Messenger Service

<\\_MSBROWSE_> 01 G Master Browser

<computername> 03 U Messenger Service

<computername> 06 U RAS Server Service

<computername> 1F U NetDDE Service

<computername> 20 U File Server Service

<computername> 21 U RAS Client Service

<computername> 22 U Exchange Interchange

<computername> 23 U Exchange Store

<computername> 24 U Exchange Directory

<computername> 30 U Modem Sharing Server Service

<computername> 31 U Modem Sharing Client Service

<computername> 43 U SMS Client Remote Control

<computername> 44 U SMS Admin Remote Control Tool

<computername> 45 U SMS Client Remote Chat

<computername> 46 U SMS Client Remote Transfer

<computername> 4C U DEC Pathworks TCPIP Service

<computername> 52 U DEC Pathworks TCPIP Service

<computername> 87 U Exchange MTA

<computername> 6A U Exchange IMC

<computername> BE U Network Monitor Agent

<computername> BF U Network Monitor Apps

<username> 03 U Messenger Service

<domain> 00 G Domain Name

<domain> 1B U Domain Master Browser

<domain> 1C G Domain Controllers

<domain> 1D U Master Browser

<domain> 1E G Browser Service Elections

<INet~Services> 1C G Internet Information Server

<IS~Computer_name> 00 U Internet Information Server

<computername> [2B] U Lotus Notes Server



Forte_$ND800ZA [20] U DCA Irmalan Gateway Service

Unique (U):

The name may have only one IP address assigned to it. On a network device, multiple occurences of a single name may appear to be registered, but the suffix will be unique, making the entire name unique.

Group (G):

A normal group; the single name may exist with many IP addresses.

Multihomed (M):

The name is unique, but due to multiple network interfaces on the same computer, this configuration is necessary to permit the registration. Maximum number of addresses is 25.

Internet Group (I):

This is a special configuration of the group name used to manage WinNT domain names.

Domain Name (D):

New in NT 4.0.

An intruder could use the table above and the output from an nbtstat against your machines to begin gathering information about them. With this information an intruder can tell, to an extent, what services are running on the target machine and sometimes what software packages have been installed. Traditionally, every service or major software package comes with it’s share of vulnerabilities, so this type of information is certainly useful to an intruder.

The next step for an intruder would be to try and list the open shares on the given computer, using the net view command, Here is an example of the net view command used against my box with the open shares C:\ and C:\MP3S\

C:\>net view \\

Shared resources at \\

Sharename    Type         Comment


C            Disk         Drive C:\

MP3S         Disk         My collection of MP3s

The command was completed successfully.

This information would give the intruder a list of shares which he would then use in conjunction with the net use command, a command used to enable a computer to map a share to it’s local drive, below is an example of how an intruder would map the C Share to a local G: drive which he could then browse:

:\>net use G: \\\C

The command was completed successfully.



However, If the intruder was targetting a large network rather than a single remote computer, the next logical step would be to glean possible usernames from the remote machine.

A network login consists of two parts, a username and a password.

Once an intruder has what he knows to be a valid list of usernames, he has half of several valid logins.

Now, using the nbtstat command, the intruder can get the login name of anyone logged on locally at that machine.In the results from the nbtstat command, entries with the <03> identifier are usernames or computernames.Gleaning usernames can also be accomplished through a null IPC session and the SID tools

The IPC$ (Inter-Process Communication) share is a standard hidden share on an NT machine which is mainly used for server to server communication.

NT machines were designed to connect to each other and obtain different types of necessary information through this share.As with many design features in any operating system, intruders have learned to use this feature for their own purposes.By connecting to this share an intruder has, for all technical purposes, a valid connection to your server.By connecting to this share as null, the intruder has been able to establish this connection without providing it with credentials.

To connect to the IPC$ share as null, an intruder would issue the following command from a command prompt:

c:\>net use \\[ip address of target machine]\ipc$ “” /user:””

If the connection is successful, the intruder could do a number of things other than gleaning a user list, but lets start with that first.

As mentioned earlier, this technique requires a null IPC session and the SID tools. Written by Evgenii Rudnyi, the SID tools come in two different parts, User2sid and Sid2user.

User2sid will take an account name or group and give you the corresponding SID. Sid2user will take a SID and give you the name of the corresponding user or group.

As a stand alone tool, this process is manual and very time consuming. is a perl script written by Mnemonix that will automate this process of SID grinding, which drastically cuts down on the time it would take an intruder to glean this information.

At this point, the intruder knows what services are running on the remote machine, which major software packages have been installed (within limits), and has a list of valid usernames and groups for that machine.Although this may seem like a ton of information for an outsider to have about your network, the null IPC session has opened other venues for information gathering.The Rhino9 team has been able to retrieve the entire native security policy for the remote machine.

Such things as account lockout, minimum password length, password age cycling, password uniqueness settings as well as every user, the groups they belong to and the individual domain restrictions for that user – all through a null IPC session.

This information gathering ability will appear in Rhino9’s soon to be released Leviathan tool. Some of the tools available now that can be used to gather more information via the IPC null session will be discussed below.

With the null IPC session, an intruder could also obtain a list of network shares that may not otherwise be obtainable.

For obvious reasons, an intruder would like to know what network shares you have available on your machines.

For this information gathering, the standard net view command is used, as follows:

c:\>net view \\[ip address of remote machine]

Depending on the security policy of the target machine, this list may or may not be denied.

Take the example below (ip address has been left out for obvious reasons):

C:\>net view \\

System error 5 has occurred.

Access is denied.

C:\>net use \\\ipc$ “” /user:“”

The command completed successfully.

C:\>net view \\

Shared resources at \\

Share name   Type         Used as  Comment


Accelerator  Disk                  Agent Accelerator share for Seagatebackup

Inetpub      Disk

mirc         Disk

NETLOGON     Disk                  Logon server share

www_pages    Disk

The command completed successfully.

As you can see, the list of shares on that server was not available until after the IPC null session had been established.

At this point you may begin to realize just how dangerous this IPC connection can be, but the IPC techniques that are known to us now are actually very basic.

The possibilities that are presented with the IPC share are just beginning to be explored.

Recommended For You

About the Author: usama

Leave a Reply

Your email address will not be published. Required fields are marked *